Modern wind turbine designs seek to incorporate various blade monitoring systems, in order to provide for reliable and controlled operation of the wind turbine. Such monitoring systems can include blade deflection monitoring systems, which are used to provide an indication of wind turbine blade deflection or flexing during turbine operation. This information can be used to monitor for the possibility of a future tower strike by the wind turbine blades, and to perform appropriate controller actions, e.g. blade pitching or turbine braking to avoid such a predicted tower strike.
An example of such a deflection monitoring system is provided in U.S. Pat. No. 7,883,316, which describes a deflection monitoring system utilizing a wireless communication network, operable to detect the position of various points along the length of the blade, and to determine blade bending from this information.
However, it has been found that such wireless monitoring systems are vulnerable to various operational factors which act to reduce the effectiveness of the monitoring system, e.g. interference from reflection or multipath effects, signal attenuation caused by passing through layers of different materials, etc. Traditionally, such monitoring systems are mounted internally of the wind turbine blade structure, and are accordingly susceptible to considerable interference due to signal reflection from the internal blade laminates and blade spars.
It is an object of the invention to provide an improved blade deflection monitoring system which is less susceptible to the above-described factors.